The present invention relates to a mobile communication system and communication method thereof, and more particularly to a mobile communication system and communication method thereof that, during handover, copies and transmits data to which transmission sequence numbers have been added from a mobile station to each of a plurality of paths going to a radio network control apparatus by way of a plurality of base stations.
A W-CDMA mobile communication system is a radio communication system in which a plurality of users shares lines, and as shown in FIG. 14, comprises: a core network (CN) 1, radio network controllers (RNC) 2, 3, radio base stations (Nodes B) 41 to 43, 51 to 53, and mobile stations (UE: User Equipment) 61 to 63. The radio network controllers RNC and radio base stations (Nodes B) are connected by wired connections using an ATM network or IP network, and the radio base stations (Nodes B) and mobile stations UE are connected by radio connections.
The core network 1 is a network for performing routing in a mobile communication system, and the core network 1 can be constructed using an ATM switching network, packet switching network, router network, etc. The core network 1 is also connected to other public networks (PSTN), which makes it possible for the mobile stations 61 to 63 to perform communication with fixed telephones.
The radio network controllers (RNC) 2, 3, are positioned as superior devices of the radio base stations (hereafter referred to as base stations) 41 to 43, 51 to 53, and they perform control (management of the radio resources that are used) of these base stations. The RNC also has a handover control function that, during handover, receives a signal from one mobile station 6i by way of the plurality of base stations, then selects data having the best quality and transmits that data to the core network 1. The radio resources for the base stations 41 to 43 are managed by the RNC 2 and the radio resources for the base stations 51 to 53 are managed by the RNC 3, while the base stations 41 to 43 and 51 to 53 perform radio communication with a mobile station 6i. When a mobile station 6i is within the radio area of a base station, a radio connection is established with that base station, and communication is performed with another communication apparatus by way of the core network 1.
An interface Iu is set as the interface between the core network 1 and RNCs 2, 3, and the interface Iub is set as the interface between the RNCs 2, 3 and each of the base stations 41 to 43, 51 to 53, and the interface Uu is set as the interface between the base stations 41 to 43, 51 to 53 and the mobile stations 61 to 63.
In this mobile communication system, in order to make high speed data transmission in the DOWN direction possible, the HSDPA (High Speed Downlink Packet Access) method is used, and in order to make high speed data transmission in the UP direction possible, the HSUPA (High Speed Uplink Packet Access) method is proposed. The HSUPA method is a broadband data transmission function for the purpose of increasing performance of a dedicated channel when a mobile station transfers data in the UP direction, and particularly is a data transmission function used in the UP direction when the mobile station is in the handover state.
FIG. 15 is a drawing that explains the logical connection of the HSUPA method during handover. The mobile station 6 is connected to the radio network controller 2 by a plurality of paths via base stations 41 to 43 and IP network 7, and the mobile station 6 makes a number of copies of the data to be transmitted that corresponds to the number of paths, then transmits the copied data to the radio network controller 2 via each of the paths. When doing this, the mobile station 6 attaches a TSN (Transmission Sequence Number) that indicates the data transmission sequence to each data. In other words, as shown in FIG. 16, when transmitting data Xn to the core network 1, the mobile station 6 copies that data Xn a number of times that corresponds to the number of paths (three in the figure), attaches the same transmission sequence number (TSN) to each copy of the data Xn and transmits the data Xn to the RNC 2 via each of the paths.
The RNC 2 receives the data Xn via each of the paths, rearranges the received data using the TSN, performs selection combining of the data and then transmits the selected data to the core network CN. In the HSPUA system, the method for the RNC to use the plurality of identical data Xn received via the plurality of paths is not regulated, and that identical plurality of received data Xn can be arbitrarily handled by any method as long as the data transmission sequence is sufficiently assured based on the TSN.
FIG. 17 is a drawing showing the layer structure of each unit in the HSUPA method, where the mobile station (UE) comprises a physical layer (PHY) of layer L1 and MAC sub layers (MAC-d, MAC-es/MAC-e) of layer L2. The MAC sub layers comprise a MAC-d (MAC-dedicated) layer, MAC-e (MAC-enhanced) layer, and MAC-es layer (MAC-enhanced sub layer). The base station (Node B) comprises a physical layer (PHY) for communicating with a mobile station by the Uu interface, and a TNL layer (Transport Network Layer) for packet communication with the radio network controller (RNC) by the Iub interface. Moreover, it comprises a MAC-e layer and EDCH FP (Enhanced DCH Frame Protocol) layer. The radio network controller comprises a TNL layer, EDCH FP layer, MAC-es layer and MAC-d layer.
FIG. 18 is a drawing that explains the procedure for creating a data (transport block) TRB by the mobile station. First, the mobile station 6 uses data that is sent via a dedicated channel DCH such as a DTCH (Dedicated Traffic Channel) or DCCH (Dedicated Control Channel) to create a data packet (MAC-d PDU data) for the MAC-d layer. This MAC-d PDU data is the same as the data packet (RLC PDU data) of the RLC sub layer. Next, the mobile station multiplexes several MAC-d PDU data, attaches a transmission sequence number TSN to the start, and creates the data (MAC-es PDU) of the MAC-es layer. After that, the mobile station multiplexes a plurality of these MAC-es PDU data, attaches a MAC-e header to the start, creates the data (MAC-e PDU) of the MAC-e layer and transmits this data as a transport block TRB to the base station by the Uu interface. The MAC-e header specifies the DDI (Data Description Identifier) and N of each MAC-es PDU data, where N specifies the number of MAC-d PDU data that is included in the MAC-es PDU data, and DDI specifies the size and ID of each MAC-d PDU data.
FIG. 19 is a drawing that explains the multiplexing relationship of the MAC-d PDU, MAC-es PDU and MAC-e PDU data, where N1 number of MAC-d PDU are multiplexed to create one MAC-es PDU, and n number of MAC-es PDU are multiplexed to create one MAC-e PDU.
When the base station receives a transport block (MAC-e PDU) from the mobile station, it creates an EDCH Iub FP frame as shown in FIG. 20 according to EDCH FP protocol, and transmits it to the RNC in a TNL layer. In other words, the base station adds the starting 5-byte data (header CRC, FSN (Frame Sequence Number), CFN (Connection Frame Sequence) and N of MAC-es PDU (number of sub frames, etc.) to the MAC-e PDU header, adds the number of retransmissions of each MAC-es PDU (N of HARQ Retransm) to the MAC-e PDU header, and creates an EDCH Iub FP frame.
As shown in FIG. 21, in the case where the radio network controller RNC receives an EDCH Iub FP frame for each logical channel, the RNC performs retransmission control (HARQ control) and, in addition by reference to the MAC-e header it divides the MAC-e PDU into MAC-es PDU, and further divides the MAC-es PDU into MAC-d PDU. Next, since there is a plurality of paths between the RNC and UE, the radio network controller RNC performs rearrangement of the received data and selection combining of the data by reference to the transmission sequence number TSN that is attached to data by the mobile station when transmitting data, thereafter gives that rearranged MAC-d PDU to the RLC sub layer (higher-order protocol), and transmits dedicated-channel data to the core network via that RLC sub layer.
In the conventional HSPUA function described above, there are the following problems.
Problem No. 1
The first problem is that, when the number of paths over which the copied data are transmitted is taken to be m, the overall used bandwidth of the Iub line between the RNC and base station increases by m times, which places a very large load on the Iub line.
As shown in FIG. 16, data is transmitted between the mobile station 6 and RNC 2 via three paths (branches). In other words, the mobile station 6 transmits the same data over the three paths #0, 1, 2, the RNC 2 performs selection combining of the data that is obtained from each path, then extracts one data flow and transmits it to the core network 1. Therefore, in the case where the mobile station 6 transmits 10 MB of data to the core network, the mobile station transmits 10 MB of data over each of the three Iub lines for a total of 30 MB, and the RNC selects just 10 MB from among that data and transmits it to the core network. When taking a comprehensive look, 20 MB of data of the 10 MB×3=30 MB of data are useless data.
Considering that the Iub line belongs to a typical IP network, the large load on that Iub line adversely affects other communication services (lost or delayed packets), and as a result, in order to perform highly reliable communication, the communication cost becomes high.
Problem No. 2
The second problem is that the data to be processed by the MAC-es processing unit of the RNC 2 increases.
Like the first problem, the amount of data input to the MAC-es processing unit increases, and the ratio between the amount of input data and amount of output data is 3:1. In order to perform selection combining of the data, the input data must be held in a buffer, however, when the amount of data that is transmitted from the mobile station 6 is large, the amount of buffered data becomes extremely large, and large processing capability is required. As a result, there is a problem in that the cost of the RNC 2 increases and the size of the RNC 2 also increases.
Problem No. 3
The third problem is that the power consumed by the mobile station to transmit data increases. HSUPA is a function for the purpose of transmitting a large amount of data, and requires that the mobile station copy data a number of times that corresponds to the number of paths. Therefore, there is a problem in that a large amount of power is required by the mobile station 6 to transmit the data.
Flow control technology has been proposed for HSDPA and HSUPA as prior art (see JP 2004-312739A). This prior art makes the size of data frames equal to or less than the size that corresponds to the scheduling interval when data frames are sent and received between the RNC and base station by the Iub interface. However, the prior art does not solve the aforementioned problems due to the transmission of data by way of a plurality of paths.